This invention relates generally to machining of surfaces and to part having machined surfaces, and more particularly, to methods and computer-aided machining of surfaces without the requirement of adaptive probing and to parts produced thereby.
Forging processes used to create some surfaces, for example, airfoil and platform surfaces, can leave excess material at intersections of edges. For example the forging process used to create airfoil and platform surfaces leaves extra material at an intersection between the airfoil lead edge (LE, or thick edge), trail edge (TE, or thin edge) and the platform. In at least one known production operation, a manual process is used to remove this excess material. In this process, referred to as “benching” or “bench blend,” a highly skilled operator grinds away material using a rotating abrasive wheel. The operator must be dedicated to the task and cannot complete any other tasks while conducting the benching operation. The operator must be highly skilled because of the proximity of the operator's hands to the grinding wheel and the high volume of parts handled in production operations. Furthermore, the blending operation must produce a smooth transition between the root fillet, airfoil and platform surfaces. No undercuts of the airfoil or platform surface are permitted since this will create stress concentrations.
Besides manual bench blending, another known technique for removing the excess material utilizes a milling machine. The region around the root fillet is probed with a Renishaw-type probe and the geometric data thus obtained is used to adjust a computer numerical control (CNC) program to adapt to the airfoil and platform surfaces. Such probes are available from Renishaw PLC, New Mills, Wooton-Under-Edge, Gloucestershire, U.K. This technique usually requires a second control unit to make essential calculations and to modify the CNC program. For high volume, short cycle time parts, the extra time required has an adverse effect on productivity.
Another known technique for removing the excess material is profile milling. Profile milling uses a ball nose end mill of the same radius as the desired fillet to generate the correct geometry. A single curve is described as the drive geometry, and the CNC program drives the end mill along this path. However, a drawback of this technique is that the end mill can be fully engaged (i.e., the entire radius of the ball is cutting), which usually increases the chance of machining chatter.